The invention relates to a method for controlling an electromechanical actuator, in particular for a gas exchange valve in an internal combustion engine.
The reference DE 195 26 683 A1 describes an actuator having an assigned actuating element which is designed as a gas exchange valve. The actuator has two electromagnets, between which an armature plate can be moved counter to the force of a restoring means by switching off the coil current on the holding electromagnet and switching on the coil current on the capturing electromagnet. The coil current of the respective capturing electromagnet is regulated to a predefined capture value, specifically during a predefined time period which is dimensioned such that the armature plate strikes a contact surface on the capturing electromagnet within the time period. The coil current of the capturing electromagnet is then regulated to a holding value.
Strict statutory regulations limit the values relating to noise emission from a motor vehicle. Accordingly, internal combustion engines must run quietly and this necessarily assumes that for an actuator to be suitable for mass production, its noise production must also be low. It is therefore the object of the present invention to provide a method for controlling an electromechanical actuator which minimizes the production of noise when an armature plate strikes an electromagnet and, at the same time, ensures reliable operation of the actuator.
The present invention is based on the discovery that in order to move the armature plate from the first or the second contact surface toward the second or first contact surface so that the speed at which the armature plate strikes the second contact surface is close to zero, exactly that quantity of energy must be supplied to the spring/mass oscillator which is removed from the latter by the electrical and mechanical losses of the spring/mass oscillator. The coil of the electromagnet can be supplied very precisely with energy when the armature plate is still outside the near region of the contact surface on the electromagnet. The invention is distinguished by the fact that a necessary first amount of electrical energy is supplied when the armature plate is still outside the near region of the contact surface on the electromagnet. A second predefined amount of electrical energy is supplied to the coil following a freewheeling operating state and before the armature plate is resting on the contact surface on the electromagnet. The coil is then controlled into the freewheeling operating state again until the armature plate comes into contact with the contact surface on the electromagnet. By means of supplying the second amount of electrical energy, which is preferably supplied when the armature plate is in the near region of the contact surface on the electromagnet, the accuracy of registering the exact point at which the armature plate strikes the contact surface on the electromagnet can be increased. The sum of the first and second amount of the electrical energy is preferably determined in such a way that it corresponds exactly to the amount of energy removed from the spring/mass oscillator by electrical and mechanical losses.